Sensors have output signals which rise between a lowest signal value (e.g., 0V) and a highest signal value (e.g., 5V). Typically, a subset range between lowest and highest sensor signal value is used to measure the sensor position. The sub range is between a low limit value, which is greater than or equal to the lowest signal value, and an upper limit value, which is less than or equal to the highest signal value. For sensor signals greater than the upper limit value, a specific state is recognized, e.g., a full load of an accelerator pedal position. For sensor signals below the lower limit, a specific state is recognized, e.g., a low idle position of an accelerator pedal position. An accelerator pedal position sensor translates position into a voltage signal, which can be used by an engine control unit. Sensors have tolerances due to manufacturing processes. The tolerance represents a specific variation of the output signal of the sensor at upper and lower limit values. A specific state of the sensor is recognized above or below the limit value of the sensor signal. The limit value is different for different sensors. For example, tolerance specified by a manufacturer for an accelerator pedal position sensor for upper limit is 89%+/−3.9% at SV (4.255V to 4.645V). The limit value for sensor1 can be anywhere in this tolerance (85.1% to 92.9% at 5V) (from 4.255V to 4.645V). Assume an actual limit value for sensor1 is at 85.1% (Uppl1 4.255V). Similarly, an actual limit value for another sensor2 with the same tolerance could be at 89% (Uppl2 4.45V). Even though both of the sensors are from the same manufacturer, due to manufacturing processes, each sensor has different upper and lower limit values. The characteristic curve and the actual limits are shown for the sensor1 and sensor2 in FIG. 1. 101 represents a characteristic curve for sensor1 and 102 represents a characteristic curve for sensor2. In an application, each sensor can be calibrated to an actual limit value for upper or lower limit value to get good accuracy. But this actual limit value has to be measured individually for both upper and lower limit and calibrated. This process of measuring actual limit values individually is costly and not advantageous in an automotive application. Another solution of the problem is to compare both sensors and set the worst case of the limit values according to the upper limit of the tolerance range so that both sensors can reach the full load of the accelerator pedal. In this example, 4.255V (85.1% at 5V) could be the limit value. This value then can be set as the actual limit value for all accelerator pedal position sensors. The underlying problem is that the sensors lose output range (A) from lower limit value to the upper limit value. In this example, the second sensor output signal reaches the upper limit value at 4.255V instead of 4.45V. The following invention solves this specific problem and extends the usable output range of the sensor automatically irrespective of the manufacturer processes.
An object of the present invention is to correct the actual limit value and to extend the usable sensor range. The example method detects for each sensor a new limit value and self learns this new limit value and thus the actual limit value of the sensor is corrected.